Abstract:

Large-scale dinoflagellate blooms started to appear in the coastal waters adjacent to the Changjiang River estuary (CRE) in the East China Sea (ECS) at the beginning of the 21st century. The oceanographic and ecological mechanisms, as well as the impacts of these harmful algal blooms (HABs), received much attention over the last decade. During the studies in the coastal waters adjacent to the CRE from 2004 to 2007, recurrent blooms of Alexandrium spp. were observed for the first time. The major causative species was identified as Alexandrium catenella. Analysis of the samples collected during the blooms of Alexandrium spp. revealed the presence of paralytic shellfish toxins (PST) dominated by low-potency N-sulfocarbamoyl toxins C1 and C2. Toxin content in the Alexandrium cells ranged from 17.08 to 33.59 fmol.cell-1. Blooms of Alexandrium spp. occurred generally in April and May, but the initiation time of the blooms varied from year to year. It’s suggested that initiation of the blooms have little connection with nutrients, as other algal blooms co-existed in this area were more significant in terms of scale and intensity. The initiation time of the blooms, however, seems to be more closely related to the seawater temperature at the bottom, which is affected by the intrusion of Taiwan Warm Current (TWC). Patches of the Alexandrium blooms were mainly found in the area of 29.0-31.0°N, 122.0-123.0°E, with water depth between 20 m and 50 m, but the distribution of the blooms varied from year to year. The distribution pattern, as well as the cell density of Alexandrium spp. during the blooms, was related to the initiation time of the blooms. It was proposed that intrusion of TWC in the sea area adjacent to the CRE may trigger the blooms of Alexandrium spp. and affect the distribution and intensity of the blooms. This hypothesis, however, requires more detailed studies on the blooms of Alexandrium spp. in this region.